Silicon Hybridization Energy Probed by Changes in Ligand Donor Strength and Molecular Rearrangements in Hexacoordinate Silicon Dichelates

Daniel Kost 1Boris Gostevskii 1Inna Kalikhman 1Mark Botoshansky 2Menahem Kaftory 2

1. Ben-Gurion University, Department of Chemistry, Beer-Sheva 84105, Israel
2. Technion, Department of Chemistry, Haifa 32000, Israel

Abstract

Neutral hydrazide-based hexacoordinate silicon bis-chelates with no halogen ligands, but with two monodentate alkyl (aryl) or hydrido ligands, are described.

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Dimethylamino complexes (1) form weakly coordinated "bicapped tetrahedral" geometries in the solid state (Figure 1), while imino-coordinated complexes (2) are more strongly bound and form distorted octahedral structures (Figure 2). The difference in donor strengths of these two nitrogen-donor types determines whether the dative bonds (in 2 and 1, respectively) provide sufficient energy to promote silicon from tetrahedral to octahedral configuration.

Hexacoordinate silacyclobutane complexes (3) have been prepared. Upon mild heating or photolyzing they undergo a skeletal rearrangement involving cleavage of the four-membered heterocycle (4). In the absence of imino α-protons (3, R1 = Ph, R2 = H) addition of the four-membered ring residue to the imino double bond takes place, forming a new chelate ring (5).

bg559colorSmall_1_1_1.jpg bg553colorSmallest_1_1.jpg
Figure 1: Crystal structure of 1 Figure 2: Crystal structure of 2
 

Presentation: invited lecture at 18th Conference on Physical Organic Chemistry, Plenary session, by Daniel Kost
See On-line Journal of 18th Conference on Physical Organic Chemistry

Submitted: 2006-05-28 06:56
Revised:   2009-06-07 00:44